Echelon strapping system



March 12, 1957 E. c. OKRESS ET AL ,7 5,340

ECHELON STRAPPING SYSTEM Filed March 11, 1953 2 Sheets-Sheet l WITNESSES: INVENTORS March 12, 1957 E. c. OKRESS ET AL ECHELON STRAPPING SYSTEM Filed March 11, 1953 Fig.5.

PRIOR A RT WITNESSES:

Fig.4.

2 Sheets-Sheet 2 INVENTORS Ernest C. Okress and Robert R. Reed.

ATTORNEY United States Patent-Q ECHELON STRAPPIN G SYSTEM Application March 11, 1953, Serial No. 341,756

Claims. c1. SIS-39.69)

Our invention relates to micro-wave oscillators and more particularly to a strapping system for oscillators of the magnetron type.

In accordance with the prior art, of which we are aware, magnetrons have been built comprising a plurality of resonant cavities arranged in a circle about a central cathode chamber. Successive cavity resonators are separated by radially extending vanes or segments of electrically conducting material. The vanes and the rest of the walls of the cavity resonators constitute the anode of the oscillators. Electrons leaving the cathode are caused to move toward the anode in cycloidal manner about the cathode by means of a D. C. voltage between the cathode and anode and an axial magnetic field in the interaction space between the cathode and anode. In so doing, they pass the regions between the vanes generating high frequency electromagnetic oscillations. These oscillations build up in amplitude in the cavity resonators. In order to reduce the mode competition difficulties associated with closely spaced resonant frequencies in such devices, strapping of'alternate vane tips together is provided. This has been accomplished by various means of which one is a set of ring straps which extend around the circle of vane tips, each ring strap making electrical contact with alternate vane tips. Thus the even-numbered vanes are connected together electrically and the odd-numbered vanes are connected together electrically. Difliculties involving loss of power have been encountered with such a strapping system which we have found to be due to arcing between the straps and the vanes. This arcing occurs because near eac'hvane there is a strap which is not directly connected to that vane. There is, therefore, a substantial high frequency potential between the unattached strap and the vane. When electrons bombard the metal surfaces of the varies and the'straps, secondary electrons are emitted; These electrons frequently strike on the .side of the vane in'the region where the strap starts to cross the vane and precipitate a vacuum metallic are between the anode vane and the inner strap. The vacuum metallic arc erodes the surfaces of the anode vane and the strap so that future electrical discharges occur more readily.

It is accordingly an object of our invention to provide a magnetron structure wherein high frequency arcing is substantially prevented. g

'It is another object of our invention to provide means for preventing arcing between the straps and the vanes of a magnetron.

Still another object of. our invention is to provide an improved strap system for a magnetron, whereby arcing is substantially prevented.

An ancillary object of our invention is to provide a new and novel electrical apparatus.

.The invention, with respect to .both the organizatio and the operation thereof, together with other objects and advantages may be best understood from the following ice v description of specific embodiments when read in connection with the accompanying drawing, in which:

Figure l is a double ring strapping system in accordance with the teachings of the prior art.

Fig. 2 is a plan view of an echelon strapping system in accordance with our invention.

'Fig. 3 is a plan view of a second echelon strapping system in accordance with our invention.

Fig. 4 is a showing in perspective, partly in cross section, of an echelon strapping system in accordance with the embodiment shown in Fig. 3.

Fig. 5 is a showing in cross section of a conventional echelon strapping system.

Fig. 6 is a showing in cross section of a recessed echelon strapping system in accordance with our invention.

Fig. 7 is an enlarged view of a strapping system in accordance with the embodiment shown in Fig. 2.

In accordance with our invention, we provide a magnetron comprising a cathode 8 surrounded by a plurality of cavity resonators 10 in a circular arrangement in the anode block 11. Successive cavity resonators are separated by radially extending vanes 12. The cavity resonators are connected electrically to the region around the cathode called the cathode chamber 14 by the passages 16 between the vanes 12.

Means are provided for placing a positive electrical potential on the anode vanes 12 and a negative potential on the cathode 8. When electrons are emitted from the cathode 3, they are caused to move toward the anode 11 by the electric field therebetween. However, a magnetic field is provided, by means well-known in the art, which causes the electrons to spiral in a cycloidal manner to ward the anode vanes 12, instead of moving directly .to

vthe anode vanes 12. The magnetic field may be provided by an electromagnet 13. The direction of rotation of the spiral is determined by the impressed magnetic field. In the specific embodiment shown in Figs. 2 and 3, the structure is designed and explained for a magnetic field setting up a counterclockwise movement. There is also a focusing action set up in the interaction space so that electrons are focused into space charge spokes that also rotate in a counterclockwise direction. The number of the space charge spokes set up within the magnetron is equal to one-half the number of vanes. At low power levels these spokes are almost radial but at higher power levels the space charge spokes are tilted in the direction of rotation with respect to the portion of the space charge spoke near the cathode. The result is that more electrons bombard the leading edge of the vanes and the inner straps. Thus, the electrons striking the anode vanes 12 on their sides 15 are in greater numbers than the electrons striking the trailing edge.

In accordance with the prior art, as shown in Fig. 1, double ring straps 19 have been provided for coupling the cavities together.

In accordance with the present invention, a plurality of straps 2G are'provided, which comprise thin strips of electrically conducting material. These straps extend into the vanes 12 in an edgewise manner as is shown in Figs. 4 and 6, and are so arranged that a first strap 22 is connected to a first vane 23 a substantial distance from the tip of that vane. The first strap then extends across the intermediate space between the first vane 23 and a second vane 25 adjacent the first vane into a recess in the second vane. The first strap passes through the recess in the second vane 25 without makingelectrical contact with that vane. The first strap then extends across the intermediate space between the second vane 25 and a third vane 27, adjacent'the second vane, tothe third vane. At the third vane 27 the first strap makes elec trical contact with-the bottom of the recess nearflthe 6 tip of the third vane 27 and at that edge of the recess in the third vane which is nearest the second vane 25.

The second strap 24 is arranged in a similar manner to that of the first strap; Thus, the second strap is' connected to the second vane 25, extends through the recess in the third vane 27, and makes contact with the fourth vane 29.

The arrangement of straps in the region of an anode vane, in accordance with one embodiment of our invention, is shown in greater detail in Fig. 4. A recess is provided in a third vane 27 near the tip 18 of that vane. Connected near the tip of the third vane is a first strap 22 comprising a thin wide strip of conducting material. The first strap 22 is connected at the leading edge of third vane 27 in a counterclockwise direction which is also the edge toward the first vane to which the other end of the first strap 22 is connected. A substantial distance from the tip 18 of the third vane 27, a third strap is connected near the opposite edge of the vane 27 from that to which the first strap 22 is connected. Passing through the recess in the third vane 27, but being separated therefrom, is a second strap 24. The second strap 24 eifectively passes between the first strap 22 and the third strap 26.

The first, second and third straps 22, 24, 26 are oriented so that their wide dimension side is presented toward the cathode. Therefore, the first strap 22 shields the second strap 24 from bombardment by electrons coming from the cathode.

Since the magnetic field through the magnetron is so oriented as to cause the electrons to move in a counterclockwise direction, the first strap 22, which is connected electrically to the third vane 27, near the tip of that vane, and near the leading edge of that vane, will have substantially no electrical potential difference from the potential of the third vane 27. There is, therefore, no tendency for arcing to occur between the first strap 22 and the third vane 27. Electrons may strike the first strap 22 and third vane 27 in the region where they are connected together without precipitating an electrical discharge. Since the second strap 24 is located in the recess in the third vane 27, behind the first strap 22, the second strap 24- is protected by the first strap 22 from electrical bombardment. There is, therefore, substantially no possibility of arcing between the second strap 24 and third vane 27. Moreover, these electrons move in cycloidal paths with circumferential velocity components directed from vane 27 toward vane 29, so those electrons which pass the left-hand edge (in Fig. 2)

of vane 27 only strike the portion of strap 24 which is near its junction with vane 29. This electron bombardment of the portion of strap 24 near the segment or vane 27 would promote arcovers. In the structure described, that portion of the strap 24 near vane 27 is completely shielded from such electron bombardment by strap 22 on the leading side on the vane 27. The strap 24 is recessed in the vane 27 and is thus protected in the vane 27 from electron bombardment. A similar shielding exists where each of the other straps passes through the channel recessed in the other vanes. Stated more generally, we thus have substantially prevented the occurrence of any arcing between a vane and that strap which passes therethrough without being connected thereto. We have also prevented arcing between any strap and the vane to which it is connected by connecting the end of the strap to the leading edge of the vane.

In accordance with another embodiment of our invention as shown in Fig. 2, the straps may make electrical contact with the vane on which they terminate at a point distant from the tip of the vane, and then extend radially along the side or edge of the vane to the tip. This configuration increases the area of thermal contact and aids in the dissipation of heat from the tip of the vane.

The structure shown in Fig. 3 results in the straps being non-straddled on portions of the vanes.

This may cause undesirable phase shifts. This difficulty may be reduced by removing certain straps (preferably two) or placing discontinuities in certain straps. In Fig. 3 a discontinuity 32 and 34 has been placed, respectively, in straps 28 and 30 for purposes of illustration.

Although we have shown and described specific embodiments of our invention, we are aware that other modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is neces tated by the prior art and the spirit of the invention.

We claim as our invention:

1. A magnetron comprising an annular anode, said anode comprising a plurality of radial extending vanes defining a plurality of cavity resonators, a cathode positioned within the central region of said annular anode, means for producing a magnetic field to cause space charge spokes emitted from said cathode to rotate in a predetermined direction, a strap comprising a thin wide strip of conducting material connected to a first of said vanes at a first radial distance from the center of said anode, said strap extending from the trailing edge of said first vane across a second of said vanes adjacent said first vane, said strap being separated from said second vane, said strap extending to a third of said vanes adjacent said second vane, said strap making electrical contact with said third vane at a radial distance less than said first radial distance, said strap recessed with a face of each of said vanes.

2. A magnetron comprising an annular anode, said anode comprising a plurality of vanes defining a plurality of cavity resonators, a cathode positioned within the central region of said annular anode, means for producing a magnetic field to cause space charge spokes emitted from said cathode to rotate in a predetermined direction, a strap connected to a first of said vanes at a substantial distance from the tip of said vane compared to the width of said strap, said strap extending from the trailing edge across a second of said vanes adjacent said first vane, said strap being separated from said second vane, said strap extending to a third of said vanes adjacent said second vane, said strap making electrical contact with said third vane at a distance less than said substantial distance from the tip of said vane, and extending along the leading edge of said third vane to the tip of said third vane.

3. A magnetron comprising an annular anode, said anode having therein a plurality of radial vanes defining a plurality of cavity resonators, a cathode positioned within the central region of said annular anode, means for producing a magnetic field to cause space charge spokes emitted from said cathode to rotate in a predetermined direction, a strap comprising a wide thin piece of metal recessed edgewise into one of said vanes a sub stantial distance from the tip thereof and making electrical contact with said vane, said strap extending from the trailing edge of said first vane through a recess in a second vane adjacent said first vane and being separated electrically from said second vane, said strap extending into a recess in a third vane and making electrical contact with said third vane at a distance from the tip thereof less than said substantial distance, a second strap of a wide flat strip of material connected to said second vane behind said first strap in the said recess in said second vane, said second strap extending from the trailing edge of said second vane through a recess in said third vane, in a region more distant from the tip of said third vane than the region where said first strap is connected to said third vane.

4. A magnetron comprising an annular anode, said anode comprising a plurality of cavity resonators arranged in a circular manner and separated by radially extending vanes, a cathode positioned within the central region of said annular anode, means for producing a magnetic field to cause space charge spokes emitted from said cathode to rotate in a predetermined direction, a first strap comprising a wide thin piece of conducting material recessed edgewise into one of said vanes and making electrical contact with said vane, a second strap connected to a second of said vanes extending from the trailing edge of said second vane and passing through a recess in said first vane, said second strap being located between said first strap and the tip of said first vane, said second strap extending from the trailing edge of said first vane and terminating on a third van-e adjacent said first vane.

5. A magnetron comprising an annular anode, said anode having a plurality of radial extending vanes defining a plurality of cavity resonators, a cathode positioned within the central region of said annular anode, means for producing a magnetic field to cause space charge spokes emitted from said cathode to rotate in a predetermined direction, a strap comprising a wide thin piece of metal connected to a first of said vanes at a 6 first radial distance from the center of said anode, said strap extending through a recess in a second vane adjacent said first vane and being separated electrically from said second vane, said strip extending from the trailing edge of said second vane and making electrical contact with a third vane at a radial distance less than said first radial distance, a second strap of a wide flat strip of material connected to said second vane behind said first strap in said recess in said second vane, said second strap extending from the trailing edge of said second vane through a recess in said third vane in a region of greater radial distance than the region where said first' strap is connected to said third vane.

References Cited in the file of this patent UNITED STATES PATENTS 2,447,537 Ronci Aug. 24, 1948 2,546,870 Sayers Mar. 27, 1951 2,547,848 Barttro Apr. 3, 1951 

